Genetic parameters were estimated based on multi-trait animal models
using the average information–restricted maximum likelihood (AI-REML) methodology. The heritability estimates (s.e.50.04 to
0.05) for the various traits for Landrace and Duroc were as follows: MG (0.19 and 0.43), FG (0.53 and 0.59), BG (0.37 and 0.58),
NCG (0.38 and 0.50), LMP (0.50 and 0.57), ADG1 (0.25 and 0.48), ADG2 (0.41 and 0.42) and FCR (0.29 and 0.42). Genetic
correlations for MG with LMP were 0.55 and 0.68, and genetic correlations between MG and ADG2 were 20.06 and 0.07 for
Landrace and Duroc, respectively. LMP and ADG2 were clearly unfavourably genetically correlated (L: 20.75 and D: 20.54). These
results showed the difficulty in jointly improving LMP and ADG2. ADG2 was unfavourably correlated with FG (L: 0.84 and D: 0.72),
thus indicating to a large extent that selection for increased growth implies selection for fatness under an ad libitum feeding regime.